The past several decades have seen remarkable advances in audio reproduction equipment, particularly equipment that allows a variety of audio tracks to be carried or transported with a user from one location to another. Such equipment includes, e.g., equipment for digitally recording, editing, mixing, producing, storing and reproducing audio tracks. Digital files are advantageous for several reasons, including the fact that error correction algorithms can be run on the files to guarantee that the audio track data in the files is properly stored, which means that the audio can be faithfully reproduced even where an underlying recording medium induces errors or where errors are induced in the copy process. Another advantage of digital files is that reproduction equipment can precisely control the speed at which the audio track is played, thereby effectively guaranteeing consistent playback. However, because of the limited processing speed of computers and digital signal processors at the time, the digital versions of the audio tracks were relatively large files, and a new means for storing large amounts of data on a relatively small media was necessitated. This lead to the development of the Audio Compact Disc, or CD.
Early CD's were designed to hold seventy-two minutes of music, almost as much as the larger cassette tapes that were in popular use at the time. By putting the CD in an appropriate reproduction device, or player, the CD could consistently reproduce audio from the audio track data stored thereon. The recording techniques used to generate the digital files also tended to sample a wider frequency range than could be stored on and reproduced from traditional magnetic media, making the reproduction more faithful than was experienced with cassette and 8-track tape players, and frequently rivaled or exceeded that of even high-end reel-to-reel systems.
Because of the many advantages of CD's over magnetic media and phonographic records, CD's quickly gained popularity. This lead to an ever-increasing number of digital audio tracks being available to individual users. As computer processing speeds and technology has continued to increase, new algorithms for storing audio tracks have emerged. One of the more popular of these new audio track storage algorithms is the Motion Picture Entertainment Group level 3 algorithm, commonly referred to as the MP3 algorithm. The MP3 algorithm uses a variety of techniques, including allowing users to vary the audio track sampling rate as the audio track is recorded, varying the number of bits used to represent a given frequency range, and the like, to generate digital audio track files that are significantly smaller than those used on CD's. This means that users can carry more audio data files on a given medium than they could in the past. For example, a typical seventy-two minute audio CD holds approximately 650 MB of data. Depending on the compression methods chosen, a 650 MB CD-ROM can easily hold several hours' worth of compressed music.
As digital storage capacity continues to increase and compression algorithms continue to advance, users are able to carry more and more of the music they like with them. This has resulted in the incorporation of audio track reproduction capabilities in an ever-increasing array of audio-capable devices, including, but not limited to, digital cameras, portable digital assistants (commonly referred to as PDA's), wireless telephones, and the like. Several other devices have been introduced into the market that are predominately used for reproduction of compressed audio tracks. These devices are generally referred to as portable music players, or PMP's. One of the most popular PMP's is the iPod, sold by Apple Computer, Inc. of Cupertino, Calif. The iPod has become popular because it has a relatively small form factor but can store many tens of gigabytes of audio files and other information on a hard disk drive stored within the PMP.